Photo-addressable substrates and photo-addressable side-group polymers with highly inducible double refraction

ABSTRACT

Disclosed is an extremely rapidly photo-addressable storage media from inherently slow photo-addressable polymers by irradiating a substrate over a large area with a light source suitable for conventional inscription so that an optical anisotropy, i.e. a double refraction with a preferential direction in the plane of the substrate occurs. If the substrates so prepared are briefly intensively irradiated, the pattern is inscribed extremely rapidly and permanently. The invention also relates to novel side-chain polymers in which high optical anisotropy can be generated by irradiation. This optical anisotropy is very heat stable.

The present invention relates to a process for the extremely rapidinscription of photo-addressable substrates, substrates prepared forthis process, and the use of such substrates in information technology.The invention also relates to photo-addressable side-group polymers inwhich a high double refraction can be induced by irradiation, so thatthey are suitable for storing optically available information or forproducing passive or optically switchable components.

Photo-addressable polymers are known (Polymers as Electrooptical andPhotooptical Active Media, V. P. Shibaev (Editor), Springer Verlag, NewYork 1995). Particularly suitable for this purpose are side-grouppolymers, of which the group of copolymers is distinguished by a verywide range of possible variations of the properties. Their particularfeature is that their optical properties such as absorption, emission,reflection, double refraction and scattering can be reversibly alteredby light induction. Such polymers have a special branched structure:side groups that can absorb electromagnetic radiation and that arejoined by parts of molecules acting as “spacers” are located on a linearbackbone. Examples of this type are the side-group polymers containingazobenzene groups according to U.S. Pat. No. 5,173,381. These substancesare characterised by the ability to exhibit double refraction in aspecific direction when irradiated with polarised light. The inscribeddouble refraction patterns can be rendered visible in polarised light.

It is also known that a locally restricted double refraction whosepreferred axis moves with the rotation of the direction of polarisationcan be inscribed at an arbitrary position in layers of these polymersusing polarised light (K. Anderle, R. Birenheide, M. Eich, J. H.Wendorff, Makromol. Chem., Rapid Commun. 10, 477-483 (1989), J. Stumpe,et al., 20. Freiburger Arbeitstagung Flüssigkristalle 1991). Theseprocesses are slow. Although in some cases the beginning of anisotropicbehaviour can be detected already after a few seconds' exposure time, asa rule minutes and even hours are necessary in order for the effect toreach its achievable maximum. In this connection the magnitude of theeffect is roughly proportional to the time employed. It is a particularfeature of optical addressing that the optic axis of the inscribeddouble refraction is vertical to that of the inscribing polarised light.The simple possibility of being able optically to extinguish inscribedinformation by rotating the direction of polarisation of the inscribinglight is based on this property. Inscription and extinction occurequally rapidly in this case; they are identical processes up to thedirection of polarisation of the employed light. This is in contrast tothe process of thermal extinction by heating the layer above the glasstransition temperature of the polymer, in which all information isextinguished at once.

In data representation, storage and processing, two fundamentallydifferent routes are followed, which may be termed serial and analog. Inthe analog route all data and information are simultaneously collectedand converted. A typical example of this is photography using a silverhalide film as an analog recording medium. This case involves exposureof a layer of photo-addressable polymers with polarised light through amaster pattern. Since all image points are developed simultaneously, theinscription (development) time is seldom critical in these processes.With serial processes however the items of information are called up insuccession. In the case of objects with a very high information density,for example images, potentially very large numbers of these image pointshave to be inscribed in succession, and the development time is thus thesummation of the development times of the individual image points. Forthis reason a high inscription rate while maintaining a sufficientstability of both the initial state of the non-inscribed regions as wellas of the final state of the inscribed regions is important. In bothprocesses the accurate reproduction of gradations of differences inbrightness (grey Stages) of the master pattern is also extremelyimportant. Hitherto it has not been possible to solve in a technicallysatisfactory manner the problem of high inscription rates by the opticalroute, since in addition to the information transmission rate, furtherboundary conditions are essential. Such boundary conditions include inparticular the stability, the extinguishability, and the ability todistinguish degrees of greyness. There are fundamental reasons for this.

As a general rule, only systems in which no mass but only fields orvectors are changed, can react extremely rapidly to control commands. Ifa mass is moved, for example in rearrangement processes or chemicalreactions, the reaction is orders of magnitude slower and is governedalso by the viscosity of the medium. For example, the switching time ofthe low-viscosity nematic rotational cells is at most in the region ofmsec, whereas a side-group copolymer takes minutes, often many hours, inorder to reach the maximum achievable double refraction.

If the reversibility of the inscribed changes is dispensed with, thenthe energy density can be chosen arbitrarily and in the limiting casethe substrate may be locally destroyed. Such materials are described forexample by G. Kämpf in Kirk-Othmer, Encyclopaedia of ChemicalTechnology, 4th ed., 14, 277-338 (1995). This process, many variants ofwhich are described in the literature, has some disadvantages however.The most important of these is that the process involves a considerableattack on the structure of the substrate, and the hole that is formed isbasically unstable. In addition there is always the problem of thevaporised material, which may be deposited anywhere in the apparatus oron the storage medium, and finally very high laser energy densities arerequired, as a rule>10⁷ mJ/m².

Since the preservation of the substrate is at the same time thenecessary condition for its re-inscribability, the light intensitycannot be increased arbitrarily; instead, the intensity must remainbelow the decomposition threshold. The stability of the material thusdefines the upper limit of the energy density. The smallest amount ofenergy that is necessary in order to produce a detectable and stablechange in the layer has been measured by Coles (in a polysiloxane) as4×10⁶ mJ/m² (C.B. McArdle in Side Chain Liquid Crystal Polymers, Editor.C. B. McArdle, Blackie Publishers, Glasgow 1989, p. 374). Assuming thatthe minimum energy for polymeric substrates is of the same order ofmagnitude, it follows, if one wishes to treat the substrate gently, thatthe side-group polymers can only be inscribed slowly (since the minimumenergy is already very close to the destruction energy), and accordinglysuch polymers are unsuitable for serial storage in real time. Thisprincipal disadvantage has up to now prevented the technical use of suchpolymers, and it is the object of the present invention to alleviatethis defect.

We have now surprisingly found that extremely rapidly addressablestorage media can be produced from the polymers that are slowlyphoto-addressable per se if the substrates are irradiated over a largearea with a light source suitable for conventional inscription, so thatan optical anisotropy is produced. Optical anisotropy means that therate of propagation of the light in the plane of the layer is dependenton the direction. This produces direction-dependent refraction,so-called double refraction. If the suitably prepared substrates areirradiated for a short time with appropriately intensive light, thedouble refraction is varied extremely rapidly and permanently, i.e. isreduced or completely extinguished. The degree of residual doublerefraction can be adjusted according to the light intensity.

Two optical processes are thus involved, which differ in their action:

In a generative first process the layer must first of all becomeanisotropically double refractive over its area. The double refraction(optical anistropy) is conventionally expressed as the difference Δn ofthe maximum, direction-dependent refractive index n at a specificwavelength.

Any light source for polarised light, for example an incandescent lampwith a connected polariser foil or preferably a laser, is suitable forgenerating the large-area anisotropic double refraction. The requiredtime depends substantially only on the power density of the lightsource, in which connection no lower limit for this is known at present.The upper limit of the power density of the light source is determinedby the destruction threshold of the material, which depends on thematerial itself and is in the range from 10⁷ to 10⁸ mW/m². The materialmay be addressed over a large area in a structureless manner orselectively, for example through a mask, though structureless addressingis preferred, especially addressing that covers the whole area of thesubstrate. The optical anisotropy Δn of the first process that isnecessary for the purposes of the invention may be very small; the onlyprecondition is that it is still measurable. Preferably the anistropy Δnproduced in the first process is at least 0.001, in particular at least0.005; it is preferably at most 0.95, in particular at most 0.8.

The second optical process relates to the use of the substrates preparedin the first optical process and comprises addressing with light of veryshort duration the material made anisotropically double refractive. Theinscribing light has a further quality however: it may be polarised orunpolarised. Polarised light is preferred whose axis lies parallel tothat of the substrate. The energy density should as a rule be 10³ to10⁷, preferably 10⁵ to 6×10⁶ mJ/m². “Short time” means that the actionof the light may last for 10⁻¹⁵ to 10⁻³, preferably 10⁻¹⁰ to 10⁻⁵ sec.The light source must be correspondingly quick, which means that laserlight sources are preferred. With this method sequential inscriptionrates of up to 100 MHz, preferably 5 to 50 MHz, are possible. Thesequential addressing means that although the absorption of the photonin the material takes place extremely rapidly, there is still sufficienttime for a dark reaction.

Extinction may take place over a large area, with the result that anunstructured pattern is produced. Patterns with structures that have adiameter of 10 nm to 20 μm, in particular 10 nm to 1 μm, in thedirection of their smallest extension are however preferred.

The inscribed information is stable, i.e. after the light source isswitched off a storable double refraction pattern is obtained that canbe read with the aid of polarised light. The change in brightness isproportional to the action of the light. The material is capable of greygradations. The inscribed information is reversible, i.e. theinformation can be re-extinguished and then re-inscribed.

The invention accordingly provides the use of flat materials with anoptical anisotropy Δn of 0.001 to 0.95 produced from photo-addressablepolymers, for storing optically available information by partiallyselectively varying the optical anisotropy. A further subject of theinvention is a process for storing patterns in the flat materials to beused according to the invention, by irradiating with light of an energydensity of 10³ to 10⁷ mJ/m² for a duration of 10⁻³ to 10⁻¹⁵ sec.

The term “optically anisotropic” within the context of the inventionmeans a difference Δn of the maximum, direction-dependent refractiveindex of at least 0.001 at a wavelength that is 30 nm shorter than thepoint at which the absorption in the long wavelength edge of the longestwavelength absorption maximum is still 1% (absorption maximum=100%).Anisotropy values that are high as possible are desired, since theypermit good results even at very low layer thicknesses. Preferred valuesof Δn are in the range from 0.05 to 0.95, in particular from 0.1 to 0.8.

The invention further provides polymers in which an optical anisotropycan be produced by pretreatment, and which can be varied by exposure fora period of 10⁻³ to 10⁻¹⁵ sec.

Suitable polymers for the production of the photo-addressable substratesare those in which a directed double refraction can be inscribed(Polymers as Electrooptical and Photooptical Active Media, V. P. Shibaev(Editor), Springer Verlag, New York 1995, Natansohn et al., Chem. Mater.1993, 403-411). In particular these are side-group polymers, preferencebeing given to the copolymers. Preferred examples of such copolymers aredescribed for example in DE-OS 43 10 368 and 44 34 966. They preferablycontain a poly(meth)acrylate main chain acting as backbone, withrepeating units

wherein R denotes hydrogen or methyl, the dots denote the coupling ofthe further units of the main chain, and the side chain is coupled tothe carbonyl group.

The invention furthermore provides polymers with side chains having thestructures described hereinafter.

The side chains branching from the main chain may correspond to theformulae

—S¹—T¹—Q¹—A  (I)

and

—S²—T²—Q²—M  (IIa)

wherein

S¹, S² denote independently of one another the atoms O, S or the radicalNR¹,

R¹ denotes hydrogen or C₁-C₄ alkyl,

T¹, T² denote independently of one another the radical (CH₂)_(n), whichmay optionally be interrupted by —O—, —NR¹— or —OSiR¹ ₂O—, and/or may besubstituted by methyl or ethyl,

n denotes the numbers 2, 3 or 4,

Q¹, Q² denote a divalent radical,

A denotes a unit that can adsorb electromagnetic radiation, and

M denotes a polarisable aromatic group containing at least 12π-electrons.

Particularly preferred are polymers in which

Q¹, Q² denote independently of one another Z¹, Z² or the group—Z¹—X—Z²—, wherein Z¹, Z² denote independently of one another the groups—S—, —SO₂, —O—, —COO—, —OCO—, —CONR¹—, —NR¹CO—, —NR¹—, —N═N—, —CH═CH—,—N═CH—, —CH═N— or the group —(CH₂)_(m) where m=1 or 2, and

X denotes a 5-membered or 6-membered cycloaliphatic, aromatic orheterocyclic ring, and in the case where Z¹=—COO— or —CONR¹— denotes adirect bond or the group —(CH═CH)_(m)—,

m having the aforementioned meaning,

A denotes the radical of a monoazo dye that absorbs in the wavelengthrange between 650 and 340 nm, and

M denotes the radical of a polarised and further polarisable aromatic,linearly structured system with at least 12 π-electrons.

Preferred radicals A correspond to the formula

wherein

R² to R⁷ independently of one another denote hydrogen, hydroxyl,halogen, nitro, cyano, C₁-C₄ alkyl, C₁-C₄ alkoxy, CF₃, CCl₃, CBr₃,SO₂CF₃, C₁-C₆ alkysulfonyl, phenylsuphonyl, C₁-C₆ alkylaminosulfonyl,phenylaminosulfonyl, aminocarbonyl, C₁-C₆ alkylaminocarbonyl,phenylaminocarbonyl or COOR¹.

Preferred radicals M correspond to the formula

wherein

R⁸ to R¹³ independently of one another denote hydrogen, hydroxyl,halogen, nitro, cyano, C₁-C₄ alkyl, C₁-C₄ alkoxy, CF₃, CCl₃, CBr₃,SO₂CF₃, C₁-C₆ alkysulfonyl, phenylsuphonyl, C₁-C₆ alkylaminosulfonyl,phenylaminosulfonyl, aminocarbonyl, C₁-C₆ alkylaminocarbonyl,phenylaminocarbonyl or COOR¹ and

Y denotes —COO—, —OCO—, —CONH—, —NHCO—, —O—, —NH—, —N(CH₃)— or a singlebond.

Preferred are amorphous polymers, i.e. polymers that do not formmacroscopically detectable liquid crystal phases. “Amorphous” denotes anoptically isotropic state. Such polymers do not scatter visible lightnor do they contain a double bond.

The compounds may be prepared in a manner known per se by copolymerisingmesogene-containing and dye-containing monomers, by a polymer-typereaction or by polycondensation. Free-radical copolymerisation of themonomers is preferred, i.e. of the monomers with mesogenic groups on theone hand and dye-containing groups on the other hand, in suitablesolvents, for example aromatic hydrocarbons such as toluene or xylene,aromatic halogenated hydrocarbons such as chlorobenzene, ethers such astetrahydrofuran and dioxane, ketones such as acetone and cyclohexanoneand/or amides such as dimethyl formamide, in the presence ofconventional radical-donating polymerisation initiators, for exampleazodiisobutyronitrile or benzoyl peroxide, at elevated temperatures, forexample at 30 to 130° C., preferably at 40 to 70° C., and as far aspossible under the exclusion of moisture and air. Purification can becarried out by precipitating or dissolving and reprecipitating theresultant side-chain copolymers from their solutions, for example withmethanol.

Whereas the groups that can absorb electromagnetic radiation as a ruleabsorb in the wavelength range of visible light, the mesogenic groups ofside-group polymers that are known up to now have an absorption maximumat a substantially shorter wavelength, preferably at wavelengths ofaround 33000 cm⁻¹; the achievable double refraction changes are lessthan 0.1. The hitherto described processes for storing information bydouble refraction changes have usually been described as reversible,i.e. with a temperature rise produced by light or heat the storedinformation can be extinguished again; the use of light may offer theadvantage of a locally restricted extinguishability, which is why thisvariant is sometimes preferred. The principal method of extinction byadding energy in the form of heat of course at the same time runs therisk of insufficient heat stability of the inscribed information;indeed, this is a disadvantage of the previously known prior art. Manycompounds of this type thus have the disadvantage that the inscribeddouble refractions are not heatstable; at elevated temperatures,especially on approaching the glass transition temperature, the doublerefraction becomes weaker and finally disappears completely.Advantageous information carriers are accordingly those in which thestability of the inscribed information is as temperature insensitive aspossible.

It has now been found that superior side-chain polymers are formed ifthe side chains are chosen so that their absorption maxima are at aspecified distance from one another. In these new polymers informationthat is extremely heat stable can be inscribed using light.

The invention accordingly also provides polymers that carry side chainsof different types on a main chain acting as a backbone, both of whichcan adsorb electromagnetic radiation (for one type at least, preferablyof the wavelength of visible light), provided that the absorption maximaof the different side chains are at a distance of at least 200,preferably at least 500, and most 10,000, preferably at at most 9,000cm¹, from one another.

Preferred polymers according to the invention carry on a main chainacting as a backbone covalently bonded side groups branching therefromand having the formulae

—S¹—T¹—Q¹—A  (I)

and

—S²—T²—Q²—P  (IIb)

wherein

S¹, S² denote independently of one another oxygen, sulfur or NR¹,

R¹ denotes hydrogen or C₁-C₄ alkyl,

T¹, T² denote independently of one another the radical (CH₂)_(n), whichmay optionally be interrupted by —O—, —NR¹— or —OSiR¹ ₂O—, and/or mayoptionally be substituted by methyl or ethyl,

n denotes the numbers 2, 3 or 4,

Q¹, Q² independently of one another denote a divalent radical,

A, P independently of one another denote a unit that can adsorbelectromagnetic radiation,

with the proviso that the absorption maxima of the radicals —Q¹—A and—Q²—P are at a distance of at least 200, preferably at least 500, and atmost 10 000, preferably at most 9 000 cm⁻¹, from one another.

An essential feature of the invention is the recognition that theproperties of the polymers according to the invention are better “ifterminal groups —Q¹—A and —Q¹—P are more similar to each other.” Thisapplies in particular with respect to their electronic configuration.The agreement of the orbital symmetry of both groups should be large,but not 100%. By exciting the longer wavelength adsorbing group in thefirst excited electronic (¹S₀) state, the orbital symmetries of thegroups A and P become approximately anti-symmetrical.

The function of the radicals T¹ and T² is to ensure a specific spacingof the side-group ends from the chain acting as the backbone. They aretherefore also termed “spacers”.

The radicals Q¹ and Q² join the terminal groups A and P to the spacersT¹ and T², which in turn form the bond to the main chain via the bondingmember S¹ and S². The special feature of the groups Q¹ and Q² is theirinfluence on both A and P on the one hand, as well as on T¹ and T² onthe other hand. The radicals Q¹ and Q² are thus of quite specialimportance: for example, a similarity of the configuration, combinedwith a relatively similar position of the absorption maxima of —Q¹—A and—Q²—P, are for example achieved if identical radicals A and P aredifferently strongly polarised by different radicals Q¹ and Q².

Preferred radicals Q¹ and Q² contain independently of one another thegroups —S—, —SO₂, —O—, —COO—, —OCO—, —CONR¹—, —NR¹CO—, —NR¹—,—(CH₂)_(m)—where m=1 or 2, a divalent 6-membered ring with optionally 1 to 2 Natoms (in which case the coupling to the radicals T¹ and A and to T² andP takes place via these N atoms) and the group Z¹—X—Z² wherein

Z¹, Z² independently of one another denote the groups —S—, —SO₂, —O—,—COO—, —OCO—, —CONR¹—, —NR¹CO—, —NR¹—, —N═N—, —CH═CH—, —N═CH—, —CH═N— orthe group —(CH₂)_(m)— where m=1 or 2, and

X denotes the naphthalene radical, a 5-membered or 6-memberedcycloaliphatic, aromatic or heterocyclic ring, the group —(CH═CH)_(m)—where m=1 or 2, or a direct bond.

Particularly preferred radicals X include 2,6-naphthylene and1,4-phenylene, and heterocyclic radicals of the structures

If X denotes a 5-membered ring system this may for example be acarbocyclic or, preferably, a heteroaromatic system and may contain upto 3 hetero atoms, preferably from the series S, N, O. Suitablerepresentatives are for example thiophene, thiazole, oxazole, triazole,oxadiazole and thiadiazol. Heterocycles with 2 hetero atoms areparticularly preferred.

If X denotes the group —(CH═CH)_(m)—, then m preferably has the value 1.

If X denotes a direct bond, the resultant compounds then are for exampleoxalic acid derivatives or urea derivatives, or carbamates (Z selectedfrom Z¹ and Z²).

The preferred meanings of Z¹—X—Z² are benzoic acid amide radicals andbenzoic acid ester radicals of the type —O—C₆H₄—COO—, —O—C₆H₄—CO—NR¹—,—NR¹—C₆H₄—COO—, —NR¹—C₆H₄—CO—NR¹—, as well as fumaric acid ester andfumaric acid amide radicals of the type —OCO—CH═CH—OCO— and—NR¹—CO—CH═CH—CO—NR¹.

Q¹ particularly preferably denotes the groups —Z¹—C₆H₄—N═N— and Q²denotes the group —Z¹—C₆H₄—CO—NH—.

The groups —Q¹—A should have absorption maxima in the wavelength rangefrom 15000 to 28000 cm⁻¹, and the groups —Q²—P should have absorptionmaxima in the wavelength range from 16000 to 29000 cm⁻¹. For thepurposes of the present invention A and P as well as Q¹ and Q² aredefined so that the longer wavelength absorbing unit is termed —Q¹—A,while the shorter wavelength adsorbing unit is termed —Q²—P.

Preferred radicals A and P include mononuclear and polynuclear radicals,for example cinnamic acid, biphenyl, stilbene and azo dye radicals,benzoic acid anilides or heterocyclic type analogues, preferably monoazodye radicals.

Particularly preferred radicals A and P correspond to the formula

—E—N=N—G  (III)

wherein

G denotes a monovalent aromatic or heterocyclic raadical and

E denotes a bivalent aromatic or heterocyclic radical.

In the case of E suitable aromatic radicals preferably contain 6 to 14 Catoms in the aromatic ring, which may be singly or multiply substitutedby C₁-C₁₂ alkyl, C₁-C₁₂ alkoxy, hydroxy, halogen (in particular F, Cl,Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (R=C₁-C₆ alkyl,cyclohexyl, benzyl, phenyl), C₅-C₁₂ cycloalkyl, C₁-C₁₂ alkylthio, C₁-C₆alkylsulfonyl, C₆-C₁₂ arylsulfonyl, aminosulfonyl, C₁-C₆alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C₁-C₆alkylaminocarbonyl, phenylaminocarbonyl, C₁-C₄ alkylamino, di-C₁-C₄alkylamino, phenylamino, C₁-C₅ acylamino, C₁-C₄ alkylsulfonylamino,mono- or di-C₁-C₄ alkylaminocarbonylamino, C₁-C₄ alkoxycarbonylamino ortrifluoromethylsulfonyl.

In the case of E suitable heterocyclic radicals preferably contain 5 to14 ring atoms, of which 1 to 4 hetero atoms are from the seriesnitrogen, oxygen, sulfur, the heterocyclic ring system being able to besingly or multiply substituted by C₁-C₁₂ alkyl, C₁-C₁₂ alkoxy, hydroxy,halogen (in particular F, Cl, Br), amino, nitro, trifluoromethyl, cyano,carboxy, COOR (R=C₁-C₆ alkyl, cyclohexyl, benzyl, phenyl), C₅-C₁₂cycloalkyl, C₁-C₁₂ alkylthio, C₁-C₆ alkylsulfonyl, C₆-C₁₂ arylsulfonyl,aminosulfonyl, C₁-C₆ alkylaminosulfonyl, phenylaminosulfonyl,aminocarbonyl, C₁-C₆ alkylaminocarbonyl, phenylaminocarbonyl, C₁-C₄alkylamino, di-C₁-C₄ alkylamino, phenylamino, C₁-C₅ acylamino, C₁-C₄alkylsulfonylamino, mono- or di-C₁-C₄ alkylaminocarbonylamino, C₁-C₄alkoxycarbonylamino or trifluoromethylsulfonyl.

In the case of G suitable aromatic radicals preferably contain 6 to 14 Catoms in the aromatic ring, which may be singly or multiply substitutedby C₁-C₁₂ alkyl, C₁-C₁₂ alkoxy, hydroxy, halogen (in particular F, Cl,Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (R=C₁-C₆ alkyl,cyclohexyl, benzyl, phenyl), C₅-C₁₂ cycloalkyl, C₁-C₁₂alkylthio,C₁-C₆alkylsulfonyl, C₆-C₁₂ arylsulfonyl, aminosulfonyl, C₁-C₆alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C₁-C₆alkylaminocarbonyl, phenylaminocarbonyl, C₁-C₄ alkylamino, di-C₁-C₄alkylamino, phenylamino, C₁-C₅ acylamino, C₆-C₁₀ arylcarbonylamino,pyridylcarbonylamino, C₁-C₄ alkylsulfonylamino, C₆-C₁₂arylsulfonylamino, mono or di-C₁-C₄ alkylaminocarbonyl-amino, C₁-C₄alkoxycarbonylamino or trifluoromethylsulfonyl.

In the case of G suitable heterocyclic radicals preferably contain 5 to14 ring atoms, of which 1 to 4 hetero atoms are from the seriesnitrogen, oxygen, sulfur, the heterocyclic ring system being able to besingly or multiply substituted by C₁-C₁₂ alkyl, C₁-C₁₂ alkoxy, hydroxy,halogen (in particular F, Cl, Br), amino, nitro, trifluoromethyl, cyano,carboxy, COOR (R=C₁-C₆ alkyl, cyclohexyl, benzyl, phenyl), C₅-C₁₂cycloalkyl, C₁-C₁₂ alkylthio, C₁-C₆ alkylsulfonyl, C₆-C₁₂ arylsulfonyl,aminosulfonyl, C₁-C₆ alkylaminosulfonyl, phenylaminosulfonyl,aminocarbonyl, C₁-C₆ alkylaminocarbonyl, phenylaminocarbonyl, C₁-C₄alkylamino, di-C₁-C₄ alkylamino, phenylamino, C₁-C₅ acylamino, C₁-C₄alkylsulfonylamino, mono- or di-C₁-C₄ alkylaminocarbonylamino, C₁-C₄alkoxycarbonylamino or trifluoromethylsulfonyl.

If the radicals E or G are multiply substituted, the number ofsubstituents is governed in each case by the number of possiblesubstitution positions, the possibility of incorporating thesubstituents, and the properties of the substituted systems. The aryland acyl radicals may optionally be substituted by nitro, cyano,halogen, C₁-C₄ alkoxy or amino.

Particularly preferred radicals —E—N═N—G contain either an aromaticradical and a heterocyclic radical (i.e. either E or G are aromatic, theother radical being heterocyclic), or two aromatic radicals (i.e. both Eand G are aromatic).

The preferred radicals —E—N═N—G are azobenzene radicals of the formula

wherein

R denotes nitro, cyano, benzamido, p-chloro, p-cyano, p-nitrobenzamidoor dimethylamino, and the rings A and B may additionally be substituted.Particularly preferred radicals A and P correspond go the formula

wherein

R² to R⁶ independently of one another denote hydrogen, chlorine,bromine, trifluoromethyl, methoxy, SO₂CH₃, SO₂CF₃, SO₂NH₂, N(CH₃)₂,preferably nitro, cyano or p-chloro, p-cyano, p-nitrobenzamido, with theproviso that at least one of these radicals is not hydrogen, and

R⁷ to R¹⁰ independently of one another denote hydrogen, chlorine ormethyl.

In the case of multiple substitution of the ring A, the 2,4- and3,4-positions are preferred.

Other preferred radicals A and P correspond to the formula:

wherein

R² to R⁶ and R⁷ to R¹⁰ have the aforementioned meanings, and

R^(2′) to R^(6′) have the same meanings as R² to R⁶, althoughindependently of the latter.

Other preferred radicals A and P correspond to the formula

wherein

K, L, M independently of one another denote the atoms N, S, O oroptionally —CH₂— or —CH═, with the proviso that at least one of themembers K, L, M is a hetero atom and the ring A is saturated or contains1 or 2 double bonds, and

R⁷ to R¹¹ independently of one another have the meanings specified abovefor R⁷ to R¹⁰.

The ring A preferably denotes a thiophene, thiazole, oxazole, triazole,oxadiazole or thiadiazole radical.

Preferred radicals —Q¹—A and —Q²—P correspond to the formulae

wherein

R¹ to R¹⁰ have the meanings specified above.

Preferred groups A and P correspond to the formulae

wherein

R² denotes hydrogen or cyano,

R^(2′) denotes hydrogen or methyl,

W denotes oxygen or NR¹, and

R⁴ denotes nitro, cyano, benzamido, p-chloro, p-cyano, p-nitrobenzamidoor dimethylamino.

Common to the above formulae is the fact that substitutions in the 4-,2,4- and 3,4-positions of the ring A are particularly preferred.

For these preferred groups A and P, preferred groups —S¹—T¹—Q¹— and—S²—T²—Q² — correspond to the formulae —OCH₂CH₂O—, —OCH₂CH₂OCH₂CH₂O— and—OCH₂CH₂NR¹—.

The preferred polymers according to the invention contain only repeatingunits with the side groups I and II, and more particularly preferablythose of the formulae

where R=H or, preferably, methyl.

The corresponding preferred monomers for introducing the side groups Iand II thus correspond to the formulae

The side groups (I) and (II) are thus preferably joined to(meth)acryloyl groups CH₂═C(R)—CO— where R=hydrogen or methyl.

Preferably the main chain of the side-group polymers is formed frommonomers that carry the side groups (I), from monomers that carry theside group (II), and optionally from further monomers, in whichconnection in particular the proportion of the monomers that exhibit theside group (I) is 10 to 95 mole %, preferably 20 to 70 mole %, theproportion of the monomers that exhibit the side group (II) is 5 to 90mole %, preferably 30 to 80 mole %, and the proportion of the furthermonomers is 0 to 50 mole %, in each case referred to the sum of allincorporated monomer units.

As “further” repeating units, all basic building blocks which can beincorporated chemically into the side-group polymer are suitable. Theysubstantially serve simply to reduce the concentration of the sidegroups I and II in the polymer and thus produce, as it were, a“dilution” effect. In the case of poly(meth)acrylates the “further”monomer include ethylenically unsaturated copolymerisable monomers thatpreferably carry α-substituted vinyl groups or β-substituted alkylgroups, preferably styrene; however, also suitable are for examplenuclear-chlorinated and alkylated or alkenylated styrenes, the alkylgroups being able to contain 1 to 4 carbon atoms and the alkenyl groupsbeing able to contain 2 to 4 carbon atoms, for example vinyl toluene,divinyl benzene, α-methyl styrene, tert.-butyl styrenes, chlorinatedstyrenes; vinyl esters or carboxylic acids with 2 to 6 carbon atoms,preferably vinyl acetate, vinyl pyridine, vinyl naphthalene, vinylcyclohexane, acrylic acid and methacrylic acid and/or their esters(preferably vinyl, allyl and methallyl esters) with 1 to 4 carbon atomsin the alcohol component, their amides and nitrites, maleic anhydride,maleic acid semi-esters and dyesters with 1 to 4 carbon atoms in thealcohol component, maleic acid semi-amides and diamides and cyclicimides such as N-methyl maleimide or N-cyclohexyl maleimide, allylcompounds such as allyl benzene and allyl esters such as allyl acetate,phthalic acid diallyl esters, isophthalic acid diallyl esters, fumaricacid diallyl esters, allyl carbonates, diallyl carbonates, triallylphosphate and triallyl cyanurate.

Preferred “further” monomers correspond to the formula

wherein

R¹² denotes an optionally branched C₁-C₆ alkyl radical or a radicalcontaining at least one further acrylic radical.

The polymers according to the invention may also contain more than oneside group that falls under the definition of (I), or more than one sidegroup that falls under the definition of (IIa) and (IIb), or severalside groups that fall under the definition of both (I) and (IIa) and(IIb).

The polymers according to the invention preferably have glass transitiontemperatures Tg of at least 40° C. The glass transition temperature maybe determined for example according to B. Vollmer, Grundriβ derMakromolekularen Chemie (Foundations of Macromolecular Chemistry), pp.406 to 410, Springer-Verlag, Heidelberg 1962).

The polymers according to the invention generally have a weight averagemolecular weight of 3000 to 2000000, preferably 5000 to 1500000, asdetermined by gel permeation chromatography (calibrated withpolystyrene).

Structural elements with a high dimensional anisotropy and highmolecular polarisability anisotropy are the prerequisite for high valuesof the optical anisotropy. By means of the structure of the polymers theintermolecular interactions of the structural elements (I) and (IIa) and(IIb) are adjusted so that the formation of liquid crystal order statesis suppressed, and optically isotropic, transparent non-scattering filmscan be produced. On the other hand the intermolecular interactions mustnevertheless be strong enough so that, on irradiation with polarisedlight, a photochemically induced, co-operative, directed re-orientationprocess of the side groups is effected.

In the optically isotropic, amorphous polymers according to theinvention extremely high values of the optical anisotropy can be inducedby irradiation with polarised light. The measured values of the changein double refraction Δn are between 0.05 and 0.8.

As light there is preferably used linearly polarised light whosewavelength lies in the range of the absorption bands of the side groups.

The present invention also provides polymers in which double refractionchanges Δn of more than 0.15, preferably more than 0.2, and inparticular more than 0.4, can be inscribed using polarised light. Thevalue Δn should be measured as described hereinafter:

First of all in each case the absorption maxima λ_(max1) and λ_(max2)are measured in both homopolymers. A double refraction change isproduced by irradiating a film of the copolymer to be tested usinglinearly polarised light of a wavelength of (λ_(max1)+λ_(max2)):2. Forthis purpose the samples are irradiated with polarised light in thedirection of the normal to the surface. The output of the light sourceshould be 1000 mW/cm²; in the case that the copolymer is destroyed underthese conditions, the output of the light source is reduced in 100 mWsteps until the copolymer is no longer destroyed by the irradiation. Theirradiation is continued until the double refraction no longer changes.The double refraction change that is produced is measured with aselective wavelength of [(λ_(max1)+λ_(max2)):2]+350±50 [nm]. Thepolarisation of the measuring light should form an angle of 45° relativeto the direction of polarisation of the inscribing light.

The preparation of the side-group monomers and their polymerisation canbe carried out according to processes known in the literature; see forexample Makromolekulare Chemie 187, 1327-1334 (1984), SU 887 574, Europ.Polym. 18, 561 (1982) and Liq. Cryst. 2, 195 (1987), DD 276 297, DE-OS28 31 909 and 38 08 430. The polymers according to the invention aregenerally prepared by free-radical copolymerisation of the monomers insuitable solvents, for example aromatic hydrocarbons such as toluene orxylene, aromatic halogenated hydrocarbons such as chlorobenzene, etherssuch as tetrahydrofuran or dioxane, ketones such as acetone orcyclohexanone, and/or dimethyl formamide in the presence ofradical-donating polymerisation initiators, for exampleazobis(isobutyronitrile) or benzoyl peroxide, at elevated temperatures,generally at 30 to 130° C., preferably at 40 to 70° C., with exclusionof water and air as far as possible. Isolation can be carried out byprecipitation with suitable agents, for example methanol. The productscan be purified by re-precipitation, for example withchloroform/methanol.

The present invention thus also provides a process for preparing theside-group polymers by copolymerisation of the corresponding monomers.

The polymers are processed into layers whose thickness is 0.1 to 500 μm,preferably 1 to 30 μm, particularly preferably 2 to 10 μm. They can becast from solution, applied with a knife, dipped, or spin coated. Theycan form self-supporting films. Preferably however they are applied tosupporting materials. This can be effected by various techniques knownper se, the process being selected according to whether a thick or thinlayer is desired. Thin layers may be produced for example by spincoating or knife application from solutions or the melt, while thickerlayers may be produced by melt pressing or extrusion.

It is possible successfully to produce isotropic films without the needfor time-consuming and costly orientation processes using externalfields and/or surface effects. The films can be applied to substrates byspin coating, immersion, casting or other technologically easilycontrollable coating processes, introduced between two transparentplates by pressing or inflow, or can simply be produced asself-supporting films by casting or extrusion. Such films can also beproduced from liquid-crystal polymers that contain the structuralelements in the aforedescribed sense, by sudden cooling, i.e. at acooling rate of>100 K/min, or by rapidly draining off the solvent.

The invention therefore also provides films (both self-supporting and inthe form of coatings) formed from the aforedescribed polymers, as wellas supports coated with these films.

The side-group polymers according to the invention are opticallyisotropic, amorphous, transparent and non-light-scattering in the glassystate of the polymers and can form self-supporting films.

Preferably however they are applied to supporting materials, for exampleglass or plastics films. This can be effected by various techniquesknown per se, the particular process being chosen according to whether athick or thin film is desired. Thin films can be produced for example byspin coating or knife application from solutions or from the melt, whilethicker films can be produced by filling preprepared cells, or by meltpressing or extrusion.

The polymers can be used for digital or analog data storage in thewidest sense, for example for optical signal processing, for Fouriertransforms and folding or in coherent optical correlation techniques.The lateral resolution is limited by the wavelength of the inscribinglight, and permits a pixel size of 0.45 to 3000 μm, preferably a pixelsize of 0.5 to 30 μm.

This property makes the polymers particularly suitable for processingimages and for information processing by means of holograms, which canbe reproduced by illuminating with a reference beam. Similarly, theinterference pattern can store two monochromatic coherent light sourceswith constant phase relation. Accordingly, three-dimensional holographicimages can be stored. The images are read by illuminating the hologramwith monochromatic, coherent light. On account of the relationshipbetween the electrical vector of the light and the associated preferreddirection in the storage medium, a higher storage density can beachieved than with a purely binary system. With analog storage values ofthe grey scale can be adjusted continuously and locally resolved.Information that is stored in an analog manner can be read in polarisedlight, and the positive or the negative image can be created dependingon the position of the polarisers. In this connection the contrast ofthe film produced by the phase displacement of the ordinary andextraordinary beam between two polarisers can be utilised, the planes ofthe polariser advantageously forming an angle of 45° relative to theplane of polarisation of the inscribing light, and the plane ofpolarisation of the analyser being either at right angles or parallel tothat of the polariser. Another possibility is to detect the angle ofdeflection of the reading light produced by induced double refraction.

The polymers can be used as optical components that can be passive orcan be actively switched, in particular for holographic optics. The highlight-induced optical anisotropy can thus be used for the electricalmodulation of the intensity and/or polarisation state of light.Accordingly, components can be produced from a polymer film byholographic structuring that have image-forming properties comparable tolenses or gratings.

The layers can be used for the serial recording of light-transmittingdata of all types, especially of images in the medical sector.

The invention therefore also provides for the use of the opticallyanisotropic substrates in information technology, especially asstructural elements and components for storing and processinginformation, preferably images, and as holographic recording material.

The percentage figures in the following examples refer, unless otherwisestated, in each case to parts by weight.

EXAMPLES Example 1

1.1 Pre-exposure

Glass plates of size 2×2 cm were spin coated with a solution of thepolymer with repeating units of the following formulae:

In order to achieve as homogeneous a pre-exposure as possible, theplates were pre-exposed (from a distance of 2 cm) on a commerciallyavailable light box (Planilux, Type LJ-S, light source: 2 light tubes(each of output 15 Watt) connected up to a foil polariser) followingwhich the transmission values were measured between two crossedpolarisers. 7.6% transmission was obtained after 1 hour's pre-exposure,and 13.7% after 2 hours' pre-exposure.

1.2 Inscription and measuring arrangement

An arrangement consisting of a linearly polarised He-Ne laser connectedto an expansion optics system, sample holder, rotatable polarisationfilter as well as an Ulbricht sphere with a connected photocellpowermeter is used to measure the inscribed double refraction. Theinscribed samples are aligned relative to the polarisation direction ofthe He-Ne laser so that the angle relative to the polarisation directionof the inscribing laser is 45°. The transmitting direction of thepolarisation filter is at right angles to the direction of the samplingHe-Ne laser. In this configuration the transmitted laser power ismeasured as a function of the inscribing power on the correspondingsample field. An additional measurement of the transmitting power at anon-inscribing sample site in the “open” position of the polarisationfilter serves for normalisation.

1.3 Inscription

Flat surfaces (flat fields) are inscribed using the aforedescribedrecorder arrangement. The polarisation direction of the inscribing laserwas at right angles to the transmitting direction of the foil polariserus ed for the pre-exposure. The relevant data of the inscribingarrangement are as follows:

Laser source: Ar-ion laser, linearly polarised. Single line operation, λ= 514.5 nm Laser power in the plane of the image max 280 mW Laser spotsize 7-8 μm Pixel size (line spacing) 5.4 μm Scanning length 7.41 mmScanning height 5.82 mm Scanning speed (in the line direction) 0.6 to23.8 m/sec

The illumination energy in the plane of the image is determined by thelaser power in the plane of the image as well as by the scanning speed.

The following change in transmission is obtained according to the energyof the inscribing light (scanning speed 23.8 m/sec; T=sampletransmission in %, E=inscribing energy in [10⁶ mJ/m²]) (see FIG. 1).

The following characteristic data can be derived from the measurementdata:

Total density stroke in the inscribing δD = 0.9 region Gradation in the“linear” part of the curve g = 1.9 Energy density to achieve δD E = 1.3× 10⁶ mJ/m²

The inscribed information is stable on storage at room temperature.

Examples 2-20

If a polymer having the repeating units shown hereinafter is employed inplace of the polymer used in Example 1, and otherwise the same procedureis employed as described in Example 1, it is found that:

In Tables 1, 2, 3 and 4 the symbols have the following meanings:

R is the substituent corresponding to formulae 2, 3, 4, 5,

λ is the wavelength of maximum absorption,

Δn is the change in double refraction achieved in a first process,

x is the content of antenna component in the copolymer,

E is the inscribing energy, and

ε is the optical density at the inscribing wavelength of 514 nm.

Repeating units

TABLE 1 R¹ R² R³ R′³ R⁴ R⁵ λ Δn x Tg E ε  2 CN CN H H CH₃ Et 490 0.04350 142 1.3 3.36  3 CN H H H H Me 472 0.029 45 141 1.6 3.19  4 CN H CN HH Me 490 0.077 50 144 1.8 2.5  5 NO₂ H Cl H H Me 490 0.057 49 129 1.91.8  6 NO₂ H H H H Et 484 0.060 48.5 124 2 1.76  7 NO₂ H H H H Me 4690.116 44 136 2.1 3  8 NO₂ H H H H Et 502 0.022 50 131 2.3 3.4  9 CH₃ HCN CN H Me 483 0.029 51 130 2.4 3.38 10 CN H H H H Me 436 0.074 58 1382.7 2.13 11 CN H H H CH₃ Et 488 0.03 50 134 2.8 3.43 12 OCH₃ H H H H Me403 0.048 75 118 3.6 0.24 13 Cl H H H H Me 412 0.042 60 99 3.7 0.52 14CN H H H H Me 452 0.057 75 133 4.1 1.75 15 Br H H H H Me 416 0.016 52137 4.2 1.51 16 CH₃ H H H H Me 408 0.05 40 133 4.3 0.57 17 OCH₃ H Cl H HMe 414 0.032 50 133 4.3 0.3 18 OCH₃ H H H H Me 407 0.079 45 128 4.5 0.219 OCH₃ H H H H Me 406 0.041 60 123 4.5 0.24 20 OCH₃ H H H H Me 4100.028 28 132 5.7 0.19

Examples 21-30

If a polymer having the repeating units shown hereinbelow is used inplace of the polymer employed in Example 1 and otherwise the sameprocedure is employed as described in Example 1, it is found that:

For the meaning of the values in the Tables, see Example 2:

TABLE 2 R¹ R² R³ R⁴ R⁵ λ Δn x E ε 21 CN H H Me H 439 0.027 60 1.2 — 22CN H CN Me H 502 0.038 40 1.4 3.34 23 CN CN H Me H 482 0.032 40 2.3 2.2424 CN H H Et Me 446 0.023 40 2.3 1.7 25 CF₃ H H Me H 420 0.041 40 2.40.6 26 SO₂CF₃ H H Me H 460 0.096 40 2.5 1.91 27 OCH H H Me H 407 0.03440 3.4 0.2 28 CN H H Me H 450 0.029 40 4.5 — 29 CN H H Me H 450 0.024 404.8 — 30 OCH₃ H H Me H 412 0.014 60 6.6 0.18

Examples 31 and 32

If a homopolymer having the repeating units shown hereinbelow is used inplace of the polymer employed in Example 1 and otherwise the sameprocedure is employed as described in Example 1, it is found that:

For the meaning of the values in the Tables, see Example 2:

TABLE 3 R¹ R² R³ R⁴ λ n x E ε 31 CN Me H — 365 0.055 100 3.5 0.2 32 CNMe Me CH₂ 365 0.042 100 3.8 0.2

Examples 33-36

If a polymer having the repeating units shown below is used in place ofthe polymer employed in Example 1 and otherwise the same procedure isemployed as described in Example 1, it is found that:

For the meaning of the values in the Table, see Example 2;

TABLE 4 R¹ R² R³ λ Δn x E ε 33 CN Et Me 443 0.042 60 1.6 1.1 34 CN Et Me444 0.039 50 1.8 1.1 35 CN Et Me 446 0.067 40 2.2 0.79 36 CF₃ Me H 4200.032 60 2.2 0.4 37 CF₃ Me H 420 0.022 70 3.3 0.4

Example 38

A sample prepared as described in Example 1 is subjected to thefollowing test cycle:

38.1 Pre-exposure of the sample on the light box with connectedpolarisation foil (exposure time: 1 hour)

38.2 Inscription with the recorder arrangement at various laser powerswith polarisation of the inscribing laser at right angles to thepolarisation of the pre-exposure

38.3 Renewed exposure of the inscribed sample on the light box withconnected polarisation foil, the transmission direction of the polariserbeing the same as in the first pre-exposure (exposure time: 7-8 hours)

38.4 Inscription with the recorder arrangement under the same conditionsas described above.

Transmission of the sample after renewed pre-exposure (see FIG. 2).

FIG. 2: Sample transmission T in [%] after renewed pre-exposure as afunction of E [10⁶ mJ/M²]:

Transmission at places at which no thermal structures have beeninscribed: filled rectangles

Transmission at the places which the thermal structures have beenproduced in the inscription process: open rectangles

FIG. 3: Transmission of the sample after renewed inscription in [%] as afunction of E [10⁶ mJ/m²]

Immediately after the inscription: open rectangles

Initial situation after the “extinction exposure”: filled rectangles(see FIG. 3)

End result:

The inscribed patterns can be completely extinguished by renewedpre-exposure at the places at which no thermal structures have beenproduced. Thermally inscribed structures remain however after theextinction exposure and reduce as a result of scattering the sampletransmission at the corresponding places.

On renewed inscription the behaviour of the sample is equivalent to theoriginal inscription test, which is illustrated by the following FIG. 4(see FIG. 4).

FIG. 4: Standardised sample transmission T[%] as a function of theinscription energy E [10⁶ mJ/m²]

After the first inscription: filled rectangles

After the second inscription: open rectangles

Example 39

Two samples produced as in Example 1 but from a polymer having repeatingunits of the formulae

are pre-exposed as described in Example 1; more specifically one sampleis pre-exposed to a transmission of 49%, and the other to a transmissionof 61%. The further procedure is as described in Example 1, and thedecrease in transmission in [%] with increasing inscription energy E in[10⁶ mJ/m²] is obtained as shown in the following FIG. 5 (see FIG. 5).

Measurement values from inscription test “49% transmission”: filledrectangles

Measurement values from inscription test “61% transmission”: openrectangles

Example 40

Preparation of the Polymers

1.1 Preparation of the Monomers

1.1.1 From Methacrylic Chloride

100 g of N-methyl-N-(2-hydroxymethyl)-aniline are dissolved in 100 ml ofchloroform. 182.6 g of triethylamine and 137.2 g of methacrylic chlorideare slowly added dropwise at 40° C. while stirring, and stirring iscontinued at 40° C. overnight. 500 ml of chloroform are then added tothe reaction solution, which is shaken with five lots of 200 ml ofwater. The organic phase is dried over anhydrous magnesium sulfate,copper (I) chloride is added thereto, and the organic phase is distilledin a high-vacuum after distilling off the solvent. The methacrylic esterof hydroxyethylaniline distils over as a water-clear liquid at 127-130°C./55 mbar. The yield is 49.5 g.

1.1.2 From Methacrylic Acid

50 ml of concentrated sulfuric acid are added dropwise at roomtemperature while stirring to a solution of 100 ml ofN-methyl-N-(2-hydroxyethyl)-aniline, 265 ml of methacrylic acid and 26.5g of hydroquinone in 398 ml of chloroform. After standing overnight themixture is heated and the reaction water is removed by azeotropicdistillation. After the solution has cooled the pH is adjusted to 7 to 8with concentrated aqueous sodium carbonate solution, and the product isextracted from this solution by shaking with ether. The product isworked up further as described above, a yield of 56 g being obtained.

1.1.3 Monomer with the Terminal Group A

7.15 g of 2,4-dicyanoaniline are diazotised with 24 g ofnitrosylsulfuric acid at 0 to 5° C. in a solution of 100 ml of glacialacetic acid, 20 ml of phosphoric acid and 7.5 ml of sulfuric acid andstirred for 1 hour. The reaction mixture is added to a solution of 15.3g of N-methyl-N-(2-methacryloyloxyethyl)-aniline and 1.5 g of urea in 60ml of glacial acetic acid, the temperature being kept at 10° C. Afterstirring briefly, the reaction mixture is adjusted to a pH of 3 withsodium carbonate solution, the precipitate is suction filtered, washedwith water and dried. 14.4 g of a red solid is obtained, which can beused directly without further purification.

1.1.4 Monomer with the terminal group P

27.6 g of 4-amino-2′, 4′-dicyanoazobenzene in 500 ml of dioxane areadded to a solution of 33 g of 4-(2-methacryloyloxy)-ethoxybenzoic acidchloride in 100 ml of dioxane, the mixture is stirred for 2 hours, andthe product is precipitated by pouring the solution into 2 l of water.The precipitate is suction filtered, dried, and purified byrecrystallising it twice from dioxane. The yield is 30.4 g of orange-redcrystals with a melting point of 215-217° C.

1.2 Preparation of the Copolymer

2.7 g of the monomer 1.1.3 and 5.19 g of the monomer 1.1.4 arepolymerised at 70° C. in 75 ml of DMF under argon as protective gas, andwith 0.39 g of azobis(isobutyronitrile) as polymerisation initiator.After 24 hours the reaction solution is filtered, the DMF is distilledoff, and the residue is boiled off with methanol to remove unreactedmonomer and is finally dried at 120° C. in a high vacuum. 7.18 g of anamorphous copolymer is obtained having a glass transition temperature of144° C., the optical properties of which are specified in Example 42.5.

Further polymers can be prepared in a similar way.

Example 41 Variation of the Spacing of the Absorption Maxima

Preparation of the measurement samples: glass plates of size 2×2 cm and1.1 mm thick are placed in a spincoater (Süss RC 5 type) and coated at2000 revs/min for absolute tetrahydrofuran. The layer is 0.9 μm thick,transparent and amorphous. Between crossed polarisers the surfaceappears uniformly dark in daylight. There are no signs of polarisingregions.

The small measurement plates are exposed with a Ar-ion laser with anoutput of 250 mW/cm² at a wavelength of 514 nm, a double refractionbeing obtained. The maximum achievable double refraction Δn in thepolymer layer is determined in two steps:

First of all the maximum inducible path difference Δλ producing abrightening between crossed polarisers is determined by measurement withan Ehringhaus compensator. The quantitative determination is performedby compensating the brightening; this is achieved by rotating a quartzcrystal placed in the beam path, which alters the optical path lengthand thus the path difference. The path difference at which thebrightening is fully compensated is now determined. The measurement mustbe carried out with light of a wavelength that lies outside theabsorption range of the compounds, in order to avoid resonance effects.As a rule a He-Ne laser of emission wavelength 633 nm is sufficient, andwith long-wave absorptions the measurement is performed with light froma diode laser of wavelength 820 nm. The selection wavelength that isused is given in the following Tables under the column heading “λ”.

In a second step the layer thickness of the polymer is measured with amechanical layer thickness measuring device (Alphastep 200, manufacturedby Tencor Instruments).

The double refraction change Δn is determined from the quotient of thepath difference Δλ and the layer thickness d:${\Delta \quad n} = \frac{\Delta \quad \lambda}{d}$

The absorption maxima are determined by evaluating the UV/visualabsorption spectra. With extreme mixtures it may happen that only onepeak can be evaluated. In such cases the non-readable value must besubstituted by the value from the corresponding 1:1-copolymer.

A similar procedure is adopted in the following examples for thepreparation of the compounds and the data measurements.

The following are obtained for the case T¹=T²; Q¹≠Q², A≠P:

m Mole-%

n Mole-%

Formula 2 λ Example v_(A) v_(P) Δv_(P−A) Δn n m mW/cm² [nm] R¹ = H; R² =CN; R³ = CN; R⁴ = CN 41.1 20900 25300 2600 0.110 70 30 250 820 R¹ = CN;R² = CN; R³ = H; R⁴ = CN 41.2 20300 27100 6800 0.183 60 40  60 633 41.320400 26700 6300 0.136 40 60  60 633 R¹ = H; R² = NO₂; R³ = H; R⁴ = CN41.4 21400 27000 5600 0.176 40 60  60 633 R¹ = NO₂; R² = NO₂; R³ = CN;R⁴ = CN 41.5 19300 25600 6300 0.190 70 30 250 820 R¹ = NO₂; R² = NO₂; R³= H; R⁴ = NO₂ 41.6 18000 26700 8700 0.106 70 30 250 820 m Mole-%

n Mole-%

Formula 3 λ Example v_(A) v_(P) Δv_(P−A) Δn m n mW/cm² [nm] R¹ = R² = H41.7  19400 27900 8300 0.197 50 50 250 820 R¹ = H; R² = CN 41.8  2000025400 5400 0.287 70 30 250 820 R¹ = CN; R² = CN 41.9  19000 25900 69000.295 60 40 250 820 R¹ = CN; R² = H 41.10 19000 27400 8200 0.318 40 60250 820 m Mole-%

n Mole-%

Formula 4 λ Example v_(A) v_(P) Δv_(P−A) Δn m n mW/cm² [nm] 41.11 1920027800 8600 0.148 50 50 250 820 Formula 5 n Mole-%

m Mole-%

λ Example v_(A) v_(P) Δv_(P−A) Δn m n mW/cm² [nm] 41.12 20700 26000 53000.120 50 50 250 820 m Mole-%

n Mole-%

Formula 6 λ Example v_(A) v_(P) Δv_(P−A) Δn m n mW/cm² [nm] 41.13 1890023400 4500 0.250 50 50 250 820

Example 42 T¹=T²; Q¹≠Q², A=P

A copolymer of the formula 7 is prepared in a similar manner to Example1 and a sample is made and measurements are carried out corresponding toExample 2. A double refraction change Δn is obtained, which is inscribedat 488 nm as follows:

λ Example v_(A) v_(P) Δv_(P−A) Δn m n mW/cm² [nm] 42.1 25000 28000 30000.232 50 50 250 633 n Mole-%

m Mole-%

Formula 8 λ Example v_(A) v_(P) Δv_(P−A) Δn m n mW/cm² [nm] R¹ = R² = R³= R⁴ = CN 42.2 20400 25800 5400 0.175 90 10 120 633 42.3 20400 254005000 0.231 80 20  60 633 42.4 20400 25300 4900 0.414 70 30  60 633 42.520400 25000 4600 0.158 60 40 120 633 R¹ = R³ = H; R² = R⁴ = NO₂ 42.619200 26700 7500 0.171 70 30 250 820 42.7 19800 25600 5800 0.145 50 50250 820 42.8 21300 25000 2700 0.116 30 30 250 820

Example 43 T¹≠T²; Q¹=Q², A=P

A copolymer of the formula

is prepared in a similar manner to Example 1.

mW/ Example V_(A) V_(P) ΔV_(P−A) Δn m n cm² λ[nm] R = CH₃ 43.1 27 000 27400 400 0.103 60 40 200 633 R = H 43.2 27 600 28 300 500 0.104 60 40 200633

Example 44 T¹=T²; Q¹=Q², A≠P

m Mole-%

n Mole-%

λ Example v_(A) v_(P) Δv_(P−A) Δn m n mW/cm² [nm] 44.1 21600 23400 18000.211 50 50 60 633

Example 45 Heat Stability

Glass plates of size 2×2 cm are coated as described in Example 1 with apolymer according to Example 3.3, and 11 fields (flat fields) areinscribed so as to produce a series of increasing transmission betweencirca. 0 and 82% with approximately equal spacing. The transmission ismeasured immediately after the inscription, and defines the initialstate. This sample is left blacked out without further protection for 2months at room temperature. Following this a further one of these platesis stored in each case for 24 hours at 60° C., 80° C. and 120° C. in adrying cabinet, and the transmission is re-measured. Four series ofvalues are thus obtained, which are compared with the initial state. Thevalues for the transmission are given in the following Table 5:

TABLE 1 Initial 2 months/ 24 h/ 24 h/ 24 h/ state 20° C. 60° C. 80° C.120° C. 82 75.4 68.9 83.6 72.2 73.8 67.2 65.6 75.4 68.9 65.6 60.7 59.064.0 54.1 50.8 45.9 52.5 55.8 49.2 54.1 45.9 52.5 55.8 44.3 19.7 24.629.5 37.7 19.7 32.8 21.3 24.6 29.5 16.4 19.7 14.8 14.8 26.2 16.4 9.8 9.813.1 16.4 11.5 6.6 6.6 11.5 11.5 9.8 0 0 6.6 8.2 4.9

The first column gives the measured values for the freshly preparedsample at room temperature, while column 2 gives the same measurementafter 2 months' storage time. The remaining columns correspond to themeasurement series after storage at the temperatures specified in thefirst line. If the values from columns 2 to 5 are plotted against thosein column 1, a straight line of gradient 1 is obtained. The grey stagesthus do not change under the effect of elevated temperature.

What is claimed is:
 1. A process for storing optically avaiableinformation comprising: providing a flat material comprising aphoto-addressable polymer having an optical anisotropy Δn from 0.001 to0.95, and irradiating with light for 10⁻⁵ to 10⁻¹⁵ seconds to vary theoptical anisotropy in a partial, selective manner.
 2. The processaccording to claim 1, wherein the energy density of the light is between10³ to 10⁷ mJ/m².